1. Field of the Invention
The present invention relates to a lens member used in, for example, light-emitting diode (LED) lighting, and the like and an optical unit including the lens member.
2. Related Art Statement
LED optical products such as lighting, projectors, flash, headlights and tail lamps of automobiles and the like, in which an LED is utilized as a light source, or basic optical devices such as a narrow directivity LED, and so on, generally use a lens for focusing or collimating light emitted from the LED. Although a convex refractive lens is usually employed for this kind of lens, adoption of a Fresnel-lens with the aim of height reduction and thinning is also proposed.
For example, there is proposed a lens for a lamp fitting which has a lattice-shaped refracting prism portion formed in a central portion of an inner surface near an optical axis, and also has a lattice-shaped reflecting prism portion formed in a peripheral portion of this lattice-shaped refracting prism portion (refer, for example, to JP 57-55002 A).
In addition, there is proposed a Fresnel-lens in which a part of the prisms of a Fresnel-lens surface acting as a light-entrance surface is formed such that a part of the entering light rays are emitted from a light-exit surface after being totally internally reflected at a non-lens surface (refer, for example, to JP S59-119340 A). Furthermore, there is proposed an optical device configured from a refractive lens portion having a lens body provided at a central portion of the optical axis and a reflecting body portion, the reflecting body portion allowing light rays to enter from an inner surface portion and totally internally reflecting the light rays at a paraboloid-shaped reflecting surface, thereby converting the light rays into a parallel beam (refer, for example, to JP H05-281402 A).
There have been proposed by the inventors of the present application a lens member and an optical device which include a Fresnel-lens surface in which a light-incident surface and a light-exit surface of a TIR lens are divided into light-incident surfaces and light-exit surfaces of a plurality of annular prisms whose positions are suitably and concentrically arranged with respect to a central axis of the lens member (see JP2010-262187A, JP2011-141450A and US2010/0284194A1).
If such a lens member including a Fresnel-lens surface as proposed above is used for a illumination device, it is often the case that a light-emitting surface of a light source including at least one LED element is smaller than the Fresnel-lens surface that is disposed to face the light-emitting surface of the light source. In this case, since a central axis of the Fresnel-lens surface of the lens member is disposed to be coincident with a center of the light-emitting surface of the light source, there is a space in a direction perpendicular to the central axis, around the light source. To utilize such a space, parts such as resistances, condensers, connecters and so on for a power circuit may be mounted in the space around the light source.
However, if parts are arranged in the space under the Fresnel-lens surface around the light source, the parts adjacent to the light source may interfere with light emitted from the light source and entering the Fresnel-lens surface. Accordingly, there is a possibility that the optical member cannot exert its optical characteristics when parts are arranged in a space around the light source.